1. Field of the Invention
The present invention relates to a high power klystron which imparts velocity modulation to electrons in an electron beam for amplification in the microwave region.
2. Description of the Prior Art
A klystron disclosed in Japanese Patent Laid-open No. Sho 62-52832 is shown in FIG. 1 in a sectional view. Referring to FIG. 1, the klystron has an electron gun 1 consisting of a cathode 11, an anode 12, and an insulating glass bulb 13 electrically insulating the cathode 11 from the anode 12. The electron gun 1 emits electron beams 2, and a collector 3 collects the electron beams 2. An input cavity resonator 4 resonates to cause velocity modulation of the electron beams 2 traveling from the electron gun 1 to the collector 3. An output cavity resonator 5 converts the beam power of the electron beams 2 subjected to density modulation for producing a compressional wave during travel through a predetermined distance after velocity modulation into microwave power. A drift tube 6 is interposed between the input cavity resonator 4 and the output cavity resonator 5 to form a drift space for the electron beams 2. The microwave power obtained by the output cavity resonator 5 is guided to an external device by an output waveguide 7. A waveguide vacuum gate valve 8 provided on the output waveguide 7 is closed while the klystron is not in use and is opened while the klystron is in use.
While the klystron is not in use, the waveguide vacuum gate valve 8 is closed to seal the klystron hermetically and the interior of the klystron is kept in a vacuum by an ion pump, not shown.
In using the klystron, the waveguide vacuum gate valve 8 is opened, the interior of the klystron is maintained in a sufficiently high vacuum by the ion pump, and then the cathode 11 of the electron gun 1 starts emitting electrons. Then, the electrons are caused to travel in the form of electron beams 2 by the voltage applied across the cathode 11 and the anode 12 (not shown). While the electron beams 2 travel through the cavity of the input cavity resonator 4, the electron beams 2 are subjected to velocity modulation by the voltage applied to the cavity of the input cavity resonator 4 (not shown). The velocity-modulated electron beams 2 undergo density modulation to produce bunching while the velocity-modulated electron beam 2 travels through a predetermined distance in the drift tube 6. The density-modulated electron beams 2 traveling through the output cavity resonator 5 induces a current and thereby the beam power of the electron beams 2 is converted into microwave power. The collector 3 absorbs the residual power of the electron beams 2.
Since the waveguide vacuum gate 8 is opened while the klystron is used, the microwave power produced by the output cavity resonator 5 is guided through the waveguide vacuum gate valve 8 to an external device by the output waveguide 7.
The waveguide vacuum gate valve 8 included in the prior art klystron thus constructed is required to maintain a vacuum in the electron gun 1 while the klystron is not in use, and to transmit the microwave power smoothly while the klystron is in use. Accordingly, the waveguide vacuum gate valve 8, in general, is of a double choke flange construction, which is complicated and expensive. Moreover, since the waveguide vacuum gate valve 8 is provided on the output waveguide 7, the magnitude of the microwave power that can be transmitted by the output waveguide 7 is limited to a relatively small magnitude by the capacity of the waveguide vacuum gate valve 8.